Semiconductor devices and methods for manufacturing the same

ABSTRACT

Semiconductor devices and methods for manufacturing the same are provided. In one embodiment, the method may include: forming a first shielding layer on a substrate, and forming one of source and drain regions with the first shielding layer as a mask; forming a second shielding layer on the substrate, and forming the other of the source and drain regions with the second shielding layer as a mask; removing a portion of the second shielding layer which is next to the other of the source and drain regions; forming a first gate dielectric layer and floating gate layer; forming a mask layer as a spacer on a sidewall of a remaining portion of the second shielding layer, and patterning the floating gate layer with the mask layer as a mask, and then removing the mask layer; and forming a second gate dielectric layer, and forming a gate conductor as a spacer on the sidewall of the remaining portion of the second shielding layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a U.S. national phase application of PCT Application No. PCT/CN2012/085826, filed on Dec. 4, 2012, entitled “SEMICONDUCTOR DEVICES AND METHODS FOR MANUFACTURING THE SAME,” which claims priority to Chinese Application No. 201210441230.2, filed on Nov. 7, 2012. Both the PCT Application and the Chinese Application are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the semiconductor field, and particularly, to semiconductor devices and methods for manufacturing the same.

BACKGROUND

With continuous scaling down of semiconductor devices, short channel effects are becoming more significant. Thus, a gate stack configuration comprising a high-K gate dielectric and a metal gate conductor is proposed. To avoid degradation of the gate stack, semiconductor devices with such a gate stack configuration are manufactured generally by means of the replacement gate process. The replacement gate process involves filling the high-K dielectric and the metal gate conductor in a gap defined between gate spacers. However, it is becoming more and more difficult to fill the high-K dielectric and the metal gate conductor in the small gap due to the scaling down of the semiconductor devices.

SUMMARY

The present disclosure provides, among others, semiconductor devices and methods for manufacturing the same.

According to an aspect of the present disclosure, there is provided a method for manufacturing a semiconductor device, comprising: forming a first shielding layer on a substrate, and forming one of source and drain regions with the first shielding layer as a mask; forming a second shielding layer on the substrate, and forming the other of the source and drain regions with the second shielding layer as a mask; removing a portion of the second shielding layer which is next to the other of the source and drain regions; forming a first gate dielectric layer and floating gate layer; forming a mask layer as a spacer on a sidewall of a remaining portion of the second shielding layer, and patterning the floating gate layer with the mask layer as a mask, and then removing the mask layer; and forming a second gate dielectric layer, and forming a gate conductor as a spacer on the sidewall of the remaining portion of the second shielding layer.

According to a further aspect of the present disclosure, there is provided a semiconductor device, comprising: a substrate; and source and drain regions and a gate stack formed on the substrate, wherein the gate stack comprises: a first gate dielectric layer; a floating gate layer; a second gate dielectric layer; and gate conductor, which is formed as a spacer on a sidewall of a dielectric layer or a gate spacer on one side of the gate stack, wherein the floating gate layer is patterned to be defined within a space between a sidewall of the gate conductor on the one side of the gate stack and the sidewall of the dielectric layer or the gate spacer and between a bottom surface of the gate conductor and a surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the present disclosure will become apparent from following descriptions of embodiments with reference to the attached drawings, in which:

FIGS. 1-11 are schematic views showing a flow of manufacturing a semiconductor device according to an embodiment of the present disclosure;

FIGS. 12-19 are schematic views showing a flow of manufacturing a semiconductor device according to a further embodiment of the present disclosure;

FIGS. 20-22 are schematic views showing a flow of manufacturing a semiconductor device according to further embodiment of the present disclosure;

FIG. 23 is a schematic view showing a semiconductor device according to a further embodiment of the present disclosure;

FIGS. 24-28 are schematic views showing, in part, a flow of manufacturing a semiconductor device according to a further embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, descriptions are given with reference to embodiments shown in the attached drawings. However, it is to be understood that these descriptions are illustrative and not intended to limit the present disclosure. Further, in the following, known structures and technologies are not described to avoid obscuring the present disclosure unnecessarily.

In the drawings, various structures according to the embodiments are schematically shown. However, they are not drawn to scale, and some features may be enlarged while some features may be omitted for sake of clarity. Moreover, shapes and relative sizes and positions of regions and layers shown in the drawings are also illustrative, and deviations may occur due to manufacture tolerances and technique limitations in practice. Those skilled in the art can also devise regions/layers of other different shapes, sizes, and relative positions as desired.

In the context of the present disclosure, when a layer/element is recited as being “on” a further layer/element, the layer/element can be disposed directly on the further layer/element, or otherwise there may be an intervening layer/element interposed therebetween. Further, if a layer/element is “on” a further layer/element in an orientation, then the layer/element can be “under” the further layer/element when the orientation is turned.

In the conventional process, after source and drain regions are formed in a substrate with the aid of a “dummy” gate stack and spacers on opposite sides of the dummy gate stack, the spacers are reserved to define a gap therebetween, and a true gate stack can be formed by filling the gap. In contrast, the present disclosure proposes a “replacement spacer” process. Specifically, after source and drain regions are formed, material layer(s) present on the side of either one of the source and drain regions is (are) reserved, and a gate stack (particularly, a gate conductor) is formed as a spacer on a sidewall of the reserved material layer(s). In this way, formation of the gate stack is done in a relatively large space (substantially corresponding to a gate region+the other of the source and drain regions). This process is easier to perform as compared with the conventional process where formation of the gate stack is done in the small gap between the spacers.

According to embodiments of the present disclosure, the source and drain regions can be formed in an active region of the substrate with the aid of shielding layer(s). For example, a first shielding layer may be adopted to mask the active region to expose a portion of the active region, which can be processed to form one of the source and drain regions. Further, a second shielding layer may be adopted to mask the active region to expose another portion of the active region, which can be processed to form the other of the source and drain regions.

The first and second shielding layers can be formed in various ways, provided that they can shield the active region to expose the respective portions of the active region. In this way, the first and second shielding layers serve as masks in the source/drain formation process. Further, the second shielding layer may comprise some portion(s) from the first shielding layer.

When the source and drain regions are formed as described above, the second shielding layer can be patterned so that a portion thereof is removed, to further expose a further portion of the active region. On the exposed further portion, a gate stack can be formed. For example, the gate stack may be formed by a spacer formation process. For convenience of patterning the second shielding layer, the second shielding layer may preferably comprise several portions of different materials, at least some of which have etching selectivity with respect to each other so that some of them can be removed selectively.

The technology of the present disclosure can be implemented in various ways, some of which will be described in the following by way of example.

Firstly, a flow of manufacturing a semiconductor device according to an embodiment of the present disclosure is described with reference to FIGS. 1-11.

As shown in FIG. 1, a substrate 100 is provided. The substrate 100 may comprise any suitable substrate, including, but not limited to, a bulk semiconductor substrate such as a bulk Si substrate, a Semiconductor On Insulator (SOI) substrate, a SiGe substrate, and the like. In the following, the substrate is described as a bulk Si substrate for convenience. On the substrate 100, Shallow Trench Isolations (STIs) 102 can be formed to isolate active regions of individual devices. For example, the STIs 102 may comprise oxide (e.g., silicon oxide). In the following, formation of a single one device is described for convenience. However, it is to be noted that the present disclosure is not limited thereto, and is also applicable to formation of two or more devices.

Next, as shown in FIG. 2, a thin oxide layer (e.g., silicon oxide) 104 is optionally formed on a surface of the substrate 100 by means of e.g. deposition. For example, the oxide layer 104 may have a thickness of about 5-10 nm, and can be used to form an Interfacial Layer (IL) subsequently. On the substrate 100 (or on the oxide layer 104 in the case where the oxide layer 104 is formed), a first shielding sub-layer 106 with a thickness of e.g. about 100-200 nm can be formed by means of e.g. deposition. For example, the first shielding sub-layer 106 may comprise nitride (e.g. silicon nitride). The first shielding sub-layer 106 can be patterned by means of e.g. Reactive Ion Etching (RIE) to cover a portion of the active region (which portion substantially corresponds to a later formed source or drain region).

In the case where the oxide layer 104 is formed, the oxide layer 104 can be selectively etched with respect to the first shielding sub-layer 106 (e.g., nitride) and the substrate 100 (e.g., bulk Si), to form an IL 108 with a thickness of e.g. about 0.5-1 nm, as shown in FIG. 3. Here, the difference in thickness between the IL 108 and the oxide layer 104 is not shown for convenience of illustration.

Further, as shown in FIG. 3, a first spacer 112 may be formed on a sidewall of the first shielding sub-layer 106. For example, the first spacer 112 is formed to have a width of about 15-60 nm to cover a portion of the active region (which portion substantially corresponds to a later formed gate region). The first spacer 112 may comprise polysilicon or amorphous silicon, for example. There are various ways to form the spacer, and detailed descriptions on formation of the spacer are omitted here.

Thus, the first shielding sub-layer 106 and the first spacer 112 (which together constitute the “first shielding layer” as described above) expose a portion of the active region. Then, one of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, this can be done as follows.

Specifically, as shown in FIG. 3 (especially, indicated by vertical arrows shown therein), extension implantation can be carried out to form an extension region 116. For example, for a p-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B; for a n-type device, the implantation can be done by implanting n-type impurities such as As or P, to form the extension region. It is to be noted that the dashed line block 116 in FIG. 3 is shown as a regular rectangular shape for convenience of illustration. In practice, the profile of the extension region 116 depends on the process, and may have no definite boundaries. Further, to improve the performance, halo implantation can be carried out before the extension implantation, as indicated by angled arrows in FIG. 3. For example, for a p-type device, the implantation can be done by implanting n-type impurities such as As or P; for a n-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B, to form a halo region (not shown).

Then, as indicated by arrows in FIG. 4, (angled) source/drain implantation can be done to form a source/drain implantation region 118. For example, for a p-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B; for a n-type device, the implantation can be done by implanting n-type impurities such as As or P, to form the source/drain implantation region. It is to be noted that the dashed line block 118 in FIG. 4 is shown as a regular rectangular shape for convenience of illustration. In practice, the profile of the source/drain implantation region 118 depends on the process, and may have no definite boundaries.

Next, as shown in FIG. 5, a second shielding sub-layer 120 may be formed on the substrate 100, to cover at least the above formed one of the source and drain regions. For example, the second shielding sub-layer 120 may comprise oxide (e.g., silicon oxide). Then, a planarization process such as Chemical Mechanical Polishing (CMP) can be performed to expose the first shielding layer (including the first shielding sub-layer 106 and the first spacer 112) to facilitate following processes.

Subsequently, as shown in FIG. 6, the first shielding sub-layer 106 can be removed by selectively etching the first shielding sub-layer 106 (e.g., silicon nitride) with respect to the first spacer 112 (e.g., polysilicon or amorphous silicon), and the second shielding sub-layer 120 and the oxide layer 104 (e.g., silicon oxide). The selective etching can be done by hot phosphoric acid, for example.

Thus, as shown in FIG. 6, the second shielding sub-layer 120 and the first spacer 112 (which together constitute the “second shielding layer” as described above) expose a portion of the active region. Then, the other of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, this can be done as follows.

Specifically, as shown in FIG. 6, extension implantation can be carried out to form an extension region 124. For example, for a p-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B; for a n-type device, the implantation can be done by implanting n-type impurities such as As or P, to form the extension region. It is to be noted that the dashed line block 124 in FIG. 6 is shown as a regular rectangular shape for convenience of illustration. In practice, the profile of the extension region 124 depends on the process, and may have no definite boundaries. Further, to improve the performance, halo implantation can be carried out before the extension implantation. For example, for a p-type device, the implantation can be done by implanting n-type impurities such as As or P; for a n-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B, to form a halo region (not shown). After that, (angled) source/drain implantation can be done to form a source/drain implantation region 126. For example, for a p-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B; for a n-type device, the implantation can be done by implanting n-type impurities such as As or P, to form the source/drain implantation region. It is to be noted that the dashed line block 126 in FIG. 6 is shown as a regular rectangular shape for convenience of illustration. In practice, the profile of the source/drain implantation region 126 depends on the process, and may have no definite boundaries.

Next, as shown in FIG. 7, annealing, such as spike annealing, laser annealing, and flash annealing, can be performed to activate the implanted impurities, to form final source and drain regions 128. Then, the first spacer 112 can be removed by selective etching. For example, the first spacer 112 (e.g., polysilicon or amorphous silicon) may be selectively removed by means of a TMAH solution. As a result, a relatively large space (substantially corresponding to the gate region+the other of the source and drain regions) is reserved on the side of the second shielding sub-layer 120, so that it is easy to form a gate stack.

Then, the gate stack can be formed as follows. Specifically, as shown in FIG. 8, a first gate dielectric layer 142 can be formed by means of e.g. deposition. For example, the first gate dielectric layer 142 may comprise a high-K gate dielectric material such as HfO₂, with a thickness of about 2-4 nm. Optionally, an IL can be rebuilt before formation of the first gate dielectric layer 142. For example, the IL (not shown) can be formed by selectively etching the oxide layer 104, as described above with reference to FIG. 3. On the first gate dielectric layer 142, a floating gate layer 144 can be formed by means of e.g. deposition. The floating gate layer 144 may comprise a metal gate conductor material, such as Ti, Co, Ni, Al, W, or any alloy thereof, or metallic material such as TiN.

According to an embodiment, the floating gate layer 144 may be patterned as follows to prevent undesirable electrical contact between the floating gate 144 and other components (such as contacts to be formed above the gate stack). Specifically, as shown in FIG. 8, a mask layer 146 may be formed on the floating gate layer 144 by means of e.g. deposition. For example, the mask layer 146 may comprise polysilicon or amorphous silicon. Next, as shown in FIG. 9, the mask layer 146 can be pattered by selective etching, such as RIE, into a mask in the form of spacer. Then, the floating gate layer 144 may be selectively etched with the spacer-like mask layer 146 in the form of mask. Optionally (but not necessarily), the first gate dielectric layer 142 may be further etched selectively.

After the floating gate layer 144 is patterned, the mask layer 146 may be removed, as shown in FIG. 10. For example, this can be done by selectively etching the mask layer 146 (e.g., polysilicon or amorphous silicon) with respect to the floating gate layer 144 (e.g., TiN) and the first gate dielectric layer 142 (e.g., HfO₂), with a TMAH solution. Then, a second gate dielectric layer 130 may be formed by e.g. deposition. On the second gate dielectric layer 130, a gate layer 134 can be formed. For example, the second gate dielectric layer 130 may comprise a high-K gate dielectric material such as HfO₂, with a thickness of about 2-4 nm, and the gate layer 134 may comprise a metal gate conductor material, such as Ti, Co, Ni, Al, W, or any alloy thereof.

Preferably, there may be a work function adjustment layer 132 sandwiched between the second gate dielectric layer 130 and the gate conductor layer 134. For example, the work function adjustment layer 132 may comprise any one of TaC, TiN, TaTbN, TaErN, TaYbN, TaSiN, HfSiN, MoSiN, RuTa, NiTa, MoN, TiSiN, TiCN, TaAlC, TiAlN, TaN, PtSi, Ni₃Si, Pt, Ru, Ir, Mo, HfRu, RuO_(x), or any combination thereof, with a thickness of about 2-10 nm.

Then, as shown in FIG. 11, the gate conductor layer 134 can be patterned into a gate conductor in the form of spacer. For example, parameters adopted in the spacer formation process, such as deposition thickness and RIE parameters, can be controlled to locate the gate conductor 134 in the form of spacer substantially between the underlying source and drain regions formed as described above.

After the gate conductor is formed, one or more of the work function adjustment layer 132, the second gate dielectric layer 130, and the first gate dielectric layer 142 can be patterned (optionally), by means of, e.g., RIE, in sequence using the gate conductor as a mask. In the example of FIG. 11, a case in which only the work function adjustment layer 132 is patterned using the gate conductor as a mask is illustrated.

Because the spacer has its size (partly) dependent on the height of the sidewall on which the spacer is formed, the gate conductor 134 (see FIG. 11) in the form of spacer is generally slightly larger than or almost equivalent to the mask layer 146 (see FIG. 9) in the form of spacer in size if they are formed under same or similar conditions. Accordingly, the floating gate layer 144 resulting from the etching with the mask layer 146 in the form of spacer as a mask generally would not extend beyond the gate conductor 134 in the form of spacer, thereby it is possible to ensure that the floating gate layer 144 is reliably sandwiched between the first gate dielectric layer 140 and the second gate dielectric layer 130 (even if they are patterned with the gate conductor 134 as a mask), and thus to avoid undesirable electrical contact.

Subsequently, an interlayer dielectric layer can be formed by means of e.g. deposition, and planarized by means of e.g., CMP. The interlayer dielectric layer may comprise oxide (e.g., silicon oxide), nitride or any combination thereof. Then, peripheral components such as contacts can be formed, and detailed descriptions thereof are omitted here.

Thus, an illustrative semiconductor device according to the present disclosure is achieved. As shown in FIG. 11, the semiconductor device may comprise the source and drain regions (128) and the gate stack (142, 140, 130, 132, 134) formed on the substrate. The gate stack, especially, the gate conductor 134, is formed as a spacer on the sidewall of the shielding layer (or, a dielectric layer) 120 on one side (the left side in the example shown in FIG. 11) of the gate stack. Because the gate stack includes the floating gate layer 144 therein, the semiconductor device can be used as a flash memory device.

As described above, the floating gate layer 144 generally would not extend beyond the gate conductor 134 in the form of spacer. In other words, the floating gate layer is located within a space between opposite side surfaces of the gate conductor 134 and the shielding layer 120 and between a bottom surface of the gate conductor 134 and the surface of the substrate 100. Specifically, the floating gate layer 144 may comprise a vertical portion extending between the sidewalls of the gate conductor 134 and the shielding layer 120 and a lateral portion extending between the surfaces of the gate conductor 134 and the substrate. Preferably, the vertical portion has an end lower than a top surface of the gate conductor 134 on the shielding layer 120 side, and the lateral portion has an end recessed with respect to an end face of the gate conductor 134 opposite to the shielding layer 120 side.

According to a further embodiment of the present disclosure, there may be a dielectric spacer (not shown) between the side wall of the shielding layer 120 and the first gate dielectric layer 142. For example, the dielectric spacer can be additionally formed on the sidewall of the second shielding sub-layer 120 after the first spacer 112 is removed (referring to the above descriptions in conjunction with FIG. 7). The dielectric spacer may comprise nitride (e.g., silicon nitride), with a thickness of about 5-20 nm. Alternatively, the dielectric spacer may be formed by the first spacer 112 which is partially removed in the process of removing the first spacer 112 (referring to the above descriptions in conjunction with FIG. 7), or may be formed on a sidewall of the first spacer 112 (referring to FIG. 4) in which case the second shielding sub-layer 120 is formed on a sidewall of the dielectric spacer (referring to FIG. 5).

Next, a flow of manufacturing a semiconductor device according to a further embodiment of the present disclosure is described with reference to FIGS. 12-19. Similar or like reference symbols in FIGS. 12-19 denote similar or like components as those shown in FIGS. 1-11. In the following, descriptions are mainly directed to differences between this embodiment and the above described embodiments.

As shown in FIG. 12, a substrate 1000 is provided. On the substrate 1000, STIs 1002 can be formed. Optionally, a thin oxide layer 1004 is formed on a surface of the substrate 1000. For details of the substrate 1000 and the oxide layer 1004, reference may be made to the above descriptions on the substrate 100 and the oxide layer 104 in conjunction with FIGS. 1-2.

On the substrate 1000 (or on the oxide layer 1004 in the case where the oxide layer 1004 is formed), a first shielding sub-layer 1006 with a thickness of e.g. about 100-200 nm can be formed by means of e.g. deposition. For example, the first shielding sub-layer 1006 may comprise nitride (e.g. silicon nitride). The first shielding sub-layer 1006 can be patterned by means of e.g. RIE to cover a portion of the active region (which portion substantially corresponds to a later formed source or drain region).

According to an embodiment, for better control of short channel effects and suppression of band-to-band leakage, a Super-Steep-Retrograded Well (SSRW) 1010 can be formed by ion implantation (indicated by arrows) with the first shielding sub-layer 1006 as a mask, as shown in FIG. 12. For example, for a p-type device, the implantation can be done by implanting n-type impurities such as As, P, or Sb; for a n-type device, the implantation can be done by implanting p-type impurities such as In, BF₂ or B, to form the SSRW. It is to be noted that the dashed line block 1010 in FIG. 12 is shown as a regular rectangular shape for convenience of illustration. In practice, the profile of the SSRW 1010 depends on the process, and may have no definite boundaries.

Subsequently, as shown in FIG. 13, a first sub-spacer 1012 may be formed on a sidewall of the first shielding sub-layer 1006. For example, the first sub-spacer 1012 is formed to have a width of about 5-50 nm to cover a portion of the active region (which portion substantially corresponds to a later formed gate region). The first sub-spacer 1012 may comprise polysilicon or amorphous silicon, for example. On a sidewall of the first sub-spacer 1012, a second sub-spacer 1014 may be formed. For example, the second sub-spacer 1014 may comprise oxide (e.g., silicon oxide), with a dimension substantially corresponding to a gate spacer (e.g., with a width of about 5-20 nm). There are various ways to form the spacers, and detailed descriptions on formation of the spacers are omitted here.

Thus, the first sub-spacer 1012 and the second sub-spacer 1014 (which together constitute a “first spacer”) and the first shielding sub-layer 1006 (which together constitute a “first shielding layer”) expose a portion of the active region. Then, one of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, a halo region (not shown), an extension region 1016 and a source/drain implantation region 1018 can be formed according to the process described above in conjunction with FIGS. 3 and 4. For details of the halo region, the extension region 1016 and the source/drain implantation region 1018, reference may be made to the above descriptions in conjunction with FIGS. 3 and 4.

Next, as shown in FIG. 14, a second shielding sub-layer 1020 may be formed on the substrate, to cover at least the above formed one of the source and drain regions. For example, the second shielding sub-layer 120 may comprise oxide (e.g., silicon oxide). Then, a planarization process such as CMP can be performed to expose the first shielding sub-layer 1006 and the first spacer (including the first sub-spacer 1012 and the second sub-spacer 1014) to facilitate following processes (as described above in conjunction with FIG. 5).

Subsequently, as shown in FIG. 15, the first shielding sub-layer 1006 can be removed by selectively etching (as described above in conjunction with FIG. 6). Then, a second spacer 1022 can be formed on a sidewall of the first sub-spacer 1012. For example, the second spacer 1022 may comprise nitride (e.g., silicon nitride), with a dimension substantially corresponding to a gate spacer (e.g., with a width of about 5-20 nm).

Thus, as shown in FIG. 15, the second shielding sub-layer 120, the first spacer (including the first sub-spacer 1012 and the second sub-spacer 1014), and the second spacer 1022 (which together constitute a “second shielding layer”) expose a portion of the active region. Then, the other of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, a halo region (not shown), an extension region 1024 and a source/drain implantation region 1026 can be formed according to the process described above in conjunction with FIG. 6. For details of the halo region, the extension region 1024 and the source/drain implantation region 1026, reference may be made to the above descriptions in conjunction with FIG. 6.

Next, as shown in FIG. 16, annealing, such as spike annealing, laser annealing, and flash annealing, can be performed to activate the implanted impurities, to form final source and drain regions 1028.

Subsequently, the second spacer 1022 and a portion of the first spacer (specifically, the first sub-spacer 1012) can be removed by selective etching to leave the second sub-spacer 1014 remained. For example, the second spacer 1022 (e.g., silicon nitride) may be selectively removed by hot phosphoric acid, and the first sub-spacer 1012 (e.g., polysilicon or amorphous silicon) may be selectively removed by means of a TMAH solution. As a result, a relatively large space (substantially corresponding to the gate region+the other of the source and drain regions) is reserved on the side of the second sub-spacer 1014, so that it is easy to form a gate stack.

Then, as shown in FIG. 17, a first gate dielectric layer 1042 and a floating gate layer 1044 can be formed sequentially, and a mask layer 1046 can be formed as a spacer (as described above in conjunction with FIGS. 8 and 9). The floating gate layer 1044 is selectively etched with the mask layer 1046 as a mask. After that, the mask layer 1046 may be removed.

Next, as shown in FIG. 18, a second gate dielectric layer 1030, a work function adjustment layer 1032, and a gate conductor 1034 in the form of spacer may be further formed (as described above in conjunction with FIGS. 10 and 11) to complete the gate stack. In the example shown in FIG. 18, the work function adjustment layer 1032 is further etched with gate conductor 1034 as a mask.

After that, as shown in FIG. 19, an interlayer dielectric layer 1036 can be formed by means of e.g. deposition, and planarized by means of e.g., CMP. The interlayer dielectric layer 1036 may comprise oxide (e.g., silicon oxide), nitride or any combination thereof.

Next, contacts 1040 corresponding to the source and drain regions can be formed. For example, the contacts 1040 may comprise metal such as W or Cu. According to an embodiment, to improve the ohmic contact, a metal silicide layer 1038 may be formed in the source and drain regions, so that the contacts 1040 are in electrical contact with the source and drain regions via the metal silicide layer 1038. For example, the metal silicide layer 1038 may comprise NiPtSi. There are various ways to form the metal silicide layer 1038 and the contacts 1040, and detailed descriptions thereof are omitted here.

Thus, an illustrative semiconductor device according to the present disclosure is achieved. As shown in FIG. 19, the semiconductor device may comprise the source and drain regions (1028) and the gate stack (1042, 1044, 1030, 1032, 1034) formed on the substrate. On one side (the left side in the example shown in FIG. 19) of the gate stack, there is the second sub-spacer 1014. The gate stack, especially, the gate conductor 1034, is formed as a spacer on the sidewall of the second sub-spacer (or the gate spacer) 1014. The semiconductor device may comprise the asymmetric SSRW 1010, which extends in the substrate under the gate stack and extends to the source or drain region on the one side of the gate stack. The floating gate layer 1044 is encapsulated by the first gate dielectric layer 1042 and the second gate dielectric layer 1030, and thus it is possible to avoid undesired electrical contact.

Next, a flow of manufacturing a semiconductor device according to a further embodiment of the present disclosure is described with reference to FIGS. 20-22. Similar or like reference symbols in FIGS. 20-22 denote similar or like components as those shown in FIGS. 1-11. In the following, descriptions are mainly directed to differences between this embodiment and the above described embodiments.

As shown in FIG. 20, a substrate 200 is provided. On the substrate 200, STIs 202 can be formed. Optionally, a thin oxide layer 204 is formed on a surface of the substrate 200. For details of the substrate 200 and the oxide layer 204, reference may be made to the above descriptions on the substrate 100 and the oxide layer 104 in conjunction with FIGS. 1-2.

On the substrate 200 (or on the oxide layer 204 in the case where the oxide layer 204 is formed), a first shielding layer 206 with a thickness of e.g. about 100-200 nm can be formed by means of e.g. deposition. For example, the first shielding layer 206 may comprise nitride (e.g. silicon nitride). The first shielding layer 206 can be patterned by means of e.g. RIE to expose a portion of the active region (which portion substantially corresponds to a later formed source or drain region). Then, one of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, a halo region (not shown), an extension region 216 and a source/drain implantation region 218 can be formed according to the process described above in conjunction with FIGS. 3 and 4. For details of the halo region, the extension region 216 and the source/drain implantation region 218, reference may be made to the above descriptions in conjunction with FIGS. 3 and 4.

Next, as shown in FIG. 21, a second shielding sub-layer 220 may be formed on the substrate, to cover at least the above formed one of the source and drain regions. For example, the second shielding sub-layer 220 may comprise oxide (e.g., silicon oxide). Then, a planarization process such as CMP can be performed to expose the first shielding layer 206, which then can be removed by selective etching. Then, a first spacer 212 may be formed on a sidewall of the second shielding sub-layer 220. For example, the first spacer 212 may be formed to have a width of about 15-60 nm, to cover a portion of the active region (which portion substantially corresponds to a later formed gate region). The first spacer 212 may comprise polysilicon or amorphous silicon, for example.

Thus, the second shielding sub-layer 220 and the first spacer 212 (which together constitute a “second shielding layer”) expose a portion of the active region. Then, the other of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, a halo region (not shown), an extension region 224 and a source/drain implantation region 226 can be formed according to the process described above in conjunction with FIG. 6. For details of the halo region, the extension region 224 and the source/drain implantation region 226, reference may be made to the above descriptions in conjunction with FIG. 6.

Next, as shown in FIG. 22, annealing, such as spike annealing, laser annealing, and flash annealing, can be performed to activate the implanted impurities, to form final source and drain regions 228.

Subsequently, the first spacer 212 can be removed by selective etching. For example, the first spacer 212 (e.g., polysilicon or amorphous silicon) may be selectively removed by means of a TMAH solution. As a result, a relatively large space (substantially corresponding to the gate region+the other of the source and drain regions) is reserved on the side of the second shielding sub-layer 220, so that it is easy to form a gate stack. For example, a first gate dielectric layer 242, a floating gate layer 244, a second gate dielectric layer 230, a work function adjustment layer 232, and a gate conductor 234 in the form of spacer can be formed sequentially (as described above in conjunction with FIGS. 8-11). Here, the floating gate layer 244 may also be etched by a mask in the form of spacer. The device shown in FIG. 20 is substantially same in structure as the device shown in FIG. 11.

Though the above descriptions in conjunction with the embodiment shown in FIGS. 20-22 do not involve an IL, operations for forming the IL can be done as described in the above embodiments.

FIG. 23 is a schematic view showing a semiconductor device according to a further embodiment of the present disclosure. The semiconductor device shown in FIG. 23 differs from that shown in FIG. 22 in that: the gate stack, especially, the gate conductor 234, is formed as a spacer on a sidewall of a second spacer 214 on one side (the left side in the example shown in FIG. 23) of the gate stack.

The device shown in FIG. 23 can be manufactured according to the process described above with reference to FIGS. 20-22. For example, the second spacer 214 can be additionally formed on the sidewall of the second shielding sub-layer 220 after the first spacer 212 is removed (referring to the above descriptions in conjunction with FIG. 22). The second spacer 214 may comprise nitride (e.g., silicon nitride), with a thickness of about 5-20 nm. Alternatively, the second spacer 214 may be formed by the first shielding layer 206 which is partially removed in the process of removing the first shielding layer 206 (referring to the above descriptions in conjunction with FIG. 21), or may be formed on a sidewall of the second shielding sub-layer 220 in which case the first spacer 212 is formed on a sidewall of the second spacer 214 (referring to FIG. 21).

Next, a flow of manufacturing a semiconductor device according to a further embodiment of the present disclosure is described with reference to FIGS. 24-28. Similar or like reference symbols in FIGS. 24-28 denote similar or like components as those shown in FIGS. 1-11. In the following, descriptions are mainly directed to differences between this embodiment and the above described embodiments.

As shown in FIG. 24, a substrate 2000 is provided. On the substrate 2000, STIs 2002 can be formed. Optionally, a thin oxide layer 2004 is formed on a surface of the substrate 2000. For details of the substrate 2000 and the oxide layer 2004, reference may be made to the above descriptions on the substrate 100 and the oxide layer 104 in conjunction with FIGS. 1-2.

On the substrate 2000 (or on the oxide layer 2004 in the case where the oxide layer 2004 is formed), a first shielding sub-layer 2006 with a thickness of e.g. about 100-200 nm can be formed by means of e.g. deposition. For example, the first shielding sub-layer 2006 may comprise nitride (e.g. silicon nitride). On a sidewall of the first shielding sub-layer 2006, a first sub-spacer 2014 can be formed. For example, the first sub-spacer 2014 may comprise oxide (e.g., silicon oxide), with a dimension substantially corresponding to a gate spacer (e.g., with a width of about 5-20 nm). Thus, the first shielding sub-layer 2006 and a first sub-spacer 2014 (which together constitute a “first shielding layer”) expose a portion of the active region (which portion substantially corresponds to a later formed source or drain region). Then, one of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, a halo region (not shown), an extension region 2016 and a source/drain implantation region 2018 can be formed according to the process described above in conjunction with FIGS. 3 and 4. For details of the halo region, the extension region 2016 and the source/drain implantation region 2018, reference may be made to the above descriptions in conjunction with FIGS. 3 and 4.

Next, as shown in FIG. 25, a second shielding sub-layer 2020 may be formed on the substrate, to cover at least the above formed one of the source and drain regions. For example, the second shielding sub-layer 2020 may comprise oxide (e.g., silicon oxide). Then, a planarization process such as CMP can be performed to expose the first shielding sub-layer 2006 and the first sub-spacer 2014. The first shielding sub-layer 2006 can be removed by selective etching.

According to an embodiment, for better control of short channel effects and suppression of band-to-band leakage, a SSRW 2010 can be formed by ion implantation with the second shielding sub-layer 2020 and the first sub-spacer 2014 as a mask, as shown in FIG. 25. For details of the SSRW 2010, reference may be made to the above descriptions in conjunction with FIG. 12.

Subsequently, as shown in FIG. 26, a second sub-spacer 2012 may be formed on a sidewall of the first sub-spacer 2014. For example, the second sub-spacer 2012 is formed to have a width of about 5-50 nm to cover a portion of the active region (which portion substantially corresponds to a later formed gate region). The second sub-spacer 2012 may comprise polysilicon or amorphous silicon, for example. On a sidewall of the second sub-spacer 2012, a third sub-spacer 2022 may be formed. For example, the third sub-spacer 2022 may comprise nitride (e.g., silicon nitride), with a dimension substantially corresponding to a gate spacer (e.g., with a width of about 5-20 nm). Thus, the second shielding sub-layer 2020, the first sub-spacer 2014, the second sub-spacer 2012, and the third sub-spacer 2022 (which together constitute a “second shielding layer”) expose a portion of the active region. Then, the other of the source and drain regions can be formed in the exposed portion of the active region by means of a source/drain formation process. For example, a halo region (not shown), an extension region 2024 and a source/drain implantation region 2026 can be formed according to the process described above in conjunction with FIG. 6. For details of the halo region, the extension region 2024 and the source/drain implantation region 2026, reference may be made to the above descriptions in conjunction with FIG. 6.

Next, as shown in FIG. 27, annealing, such as spike annealing, laser annealing, and flash annealing, can be performed to activate the implanted impurities, to form final source and drain regions 2028.

Subsequently, the second sub-spacer 2012 and the third sub-spacer 2022 can be removed by selective etching to leave the first sub-spacer 2014 remained. For example, the second sub-spacer 2012 (e.g., polysilicon or amorphous silicon) may be selectively removed by means of a TMAH solution, and the third sub-spacer 2022 (e.g., silicon nitride) may be selectively removed by hot phosphoric acid. As a result, a relatively large space (substantially corresponding to the gate region+the other of the source and drain regions) is reserved on the side of the first sub-spacer 2014, so that it is easy to form a gate stack.

The flow can continue similarly to that shown in FIGS. 17-18, and detailed descriptions thereof are omitted here. For example, the gate stack (including a first gate dielectric layer 2042, a floating gate layer 2044, a second gate dielectric layer 2030, a work function adjustment layer 2032, and a gate conductor 2034 in the form of spacer) can be formed. The floating gate layer 2044 can be etched by using a mask in the form of spacer. The resultant device is similar to that shown in FIG. 18, except that the SSRW 2010 extends to the opposite side.

Though the above descriptions in conjunction with the embodiment shown in FIGS. 24-28 do not involve an IL, operations for forming the IL can be done as described in the above embodiments.

In the above descriptions, details of patterning and etching of the layers are not described. It is to be understood by those skilled in the art that various measures may be utilized to form the layers and regions in desired shapes. Further, to achieve the same feature, those skilled in the art can devise processes not entirely the same as those described above. The mere fact that the various embodiments are described separately does not mean that means recited in the respective embodiments cannot be used in combination to advantage.

From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. In addition, many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the technology is not limited except as by the appended claims. 

I claim:
 1. A method for manufacturing a semiconductor device, comprising the steps in sequence of: forming, on a substrate, a first shielding sub-layer on the substrate and also a first spacer on a sidewall of the first shielding sub-layer; forming one of source and drain regions with the first shielding sub-layer together with the first spacer as a mask; forming a second shielding sub-layer on the substrate next to the first spacer and removing the first shielding sub-layer; forming the other of the source and drain regions with the second shielding sub-layer together with the first spacer as a mask; removing the first spacer; forming a first gate dielectric layer and a floating gate layer on the substrate with the second shielding sub-layer left thereon; forming, on the floating gate layer, a mask layer as a spacer on a sidewall of the second shielding sub-layer, and patterning the floating gate layer with the mask layer as a mask, and then removing the mask layer; and forming a second gate dielectric layer on the first gate dielectric layer and the patterned floating gate layer, and forming, on the second gate dielectric layer, a gate conductor as a spacer on the sidewall of the second shielding sub-layer.
 2. The method according to claim 1, wherein the step of forming the source or drain region comprises: performing extension implantation; and performing source/drain implantation.
 3. The method according to claim 2, wherein the step of forming the source or drain region further comprises: performing halo implantation.
 4. The method according to claim 1, wherein the mask layer has a top surface lower than that of the second shielding sub-layer.
 5. A semiconductor device, comprising: a substrate; and source and drain regions and a gate stack formed on the substrate, wherein the gate stack comprises: a first gate dielectric layer; a floating gate layer; a second gate dielectric layer; and a gate conductor, which is formed as a spacer on a sidewall of a third dielectric layer on one side of the gate stack, wherein the floating gate layer is in an “L” shape so that one leg of the “L” shape is defined within a space between a sidewall of the gate conductor on the one side and the sidewall of the third dielectric layer and has a top end lower than a top surface of the gate conductor on the one side, and that the other leg of the “L” shape is defined within a space between a bottom surface of the gate conductor and a surface of the substrate and has an end recessed with respect to an end surface of the gate conductor on the other side opposite to the one side, and wherein the source and drain regions are positioned on the one side and the other side with respect to the gate stack, respectively.
 6. The semiconductor device according to claim 5, wherein each of the first and second gate dielectric layers comprise a high-K dielectric material, and each of the floating gate layer and the gate conductor comprise a metal gate conductor material.
 7. The semiconductor device according to claim 5, further comprising a work function adjustment layer disposed between the second gate dielectric layer and the gate conductor.
 8. The semiconductor device according to claim 7, wherein the work function adjustment layer comprises any one of TaC, TiN, TaTbN, TaErN, TaYbN, TaSiN, HfSiN, MoSiN, RuTa, NiTa, MoN, TiSiN, TiCN, TaAlC, TiAlN, TaN, PtSi, Ni₃Si, Pt, Ru, Ir, Mo, HfRu, RuO_(x), or any combination thereof.
 9. The semiconductor device according to claim 5, further comprising a super-steep-retrograded well formed in the substrate, which extends to either the source side or the drain side. 